Light beam edge detection

ABSTRACT

A light beam polarized at 45* to the plane of view is split in a birefringent crystal into two components, o and ao, which are linearly polarized vertically and parallel to the plane of view respectively. An electro-optic element energized by a High Frequency source transforms the components into two oppositely circularly polarized beams so as to alternately change their direction of polarization by 90*. The alternately polarized beams are simultaneously passed through a second birefringent crystal so as to converge one beam to the other beam at a single exit site of the crystal, and in the other configuration of rotated polarization, so as to diverge the other beam so that the two beams exit at two spaced sites of the crystal spaced about the first exit site. This alternately provides a single central beam and two outer beams. When an edge separating a surface having areas of two different optical properties is brought into the range of the alternating light beams, the change in their intensities is employed to precisely locate the edge by the rate of change in intensities.

Unite/.51 States Patent Schedewie Oct. 9, 1973 LIGHT BEAM EDGE DETECTION[57] ABSTRACT [75] Inventor: Franz Joseph Schedewie, A light beampolarized at 45 to the plane of view is Boeblingen, Germany split in abirefringent crystal into two components, 0

and a0, which are linearly polarized vertically and parl l Assigneeilntel'nalionalBusmess Machines allel to the plane of view respectivelyAn electro- Colpolation, Armonk, optic element energized by a HighFrequency source [22] Filed: Jan. 12, 1972 transforms the componentsinto two oppositely circularly polarized beams so as to alternatelychange their 1 p 217,170 direction of polarization by 90. Thealternately polarized beams are simultaneously passed through a seei AIi {0 P hr Data 0nd birefringent crystal so as to converge one beam to[30] Fore pp ca I n n y P 21 02 027 9 the other beam at a single exitsite of the crystal, and 1971 Germany in the other configuration ofrotated polarization, so as to diverge the other beam so that the twobeams [52] Cl 5 s i g g ig exit at two spaced sites of the crystalspaced about the l G01 21/40 first exit site. This alternately providesa single central [51] int. C beam and two Outer beanm when an edgeSeparating [58] Field of Search ..356/114-l19, 152, 153, a Surface havinareas of two different 0 tical r 6 350/150 157- 250/219 DR P "P ties isbrought into the range of the alternating light beams, the change intheir intensities is employed to References Clted precisely locate theedge by the rate of change in in- UNITED STATES PATENTS tensities.

3,591,254 6/1971 Browne et a] 350/150 3,391,970 6/1968 Sincerbox 356/114Primary Examiner-Ronald L. Wibert Assistant ExaminerPau1 K. GodwinAtt0meyl-lenry Powers et al.

36 Claims, 13 Drawing Figures PATENTED UB1 9 I873 SHEET 10F 4 FIG.iA

FIG.I

FIG.2

PATENTEU 9'973 3.764.218

SHEET 2 [IF 4 START STOP F l G. 3 RATE OF CHANGE OF INTENSITY PATENTEUBET 91975 SHEET 3 BF 4 PIC-3.4

LIGHT BEAM EDGE DETEGTION BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to optical beam deflection andorientation, and more particularly to optical detection of an edgedemarcating areas of varying optical properties.

2. Description of the Prior Art I-Ieretofore, the existence ofpredetermined gradients of reflectivity or transparency of a surfacecould be determined by scanning the surface by means of light beams withthe reflected or the transmitted light transduced by photosensitiveelements into electrical signals, which, after appropriate processing bysuitable electrical circuits locate the edge between the varying opticalproperties of the surface. The scanning is normally accomplished bydetecting the existence of disturbances resulting from imaging of alight probe at the absolute or relative position of line edges,particularly their spacings, or across the form of an alpha-numericcharacter to be detected. It is also possible to use light beam scanningfor evaluation of images with different transitions of transparencies,reflectants, color properties, shadows, for evaluation of opticalgradient in transition of transparencies or reflectancies, or opacitiesor of color properties, and the like.

In all these forms of application, the light beam only serves as a probewhose modulation, on scanning, is transduced into electrical signalswhich are processed into required results by well-known circuittechniques.

Typical of such prior arts system is that described in AutomatischesVermessen und Protokollieren von Praezisionsmabstaeben by K. Heinecke,Maschinemarkt, 71, May 1965 page 27, which utilizes a scanning lightbeam for analysis of a transparency wherein the light beam impinges uponthe edge of a prism through which the resultant signal is split intoequal components. The difference in the components is then determined bytwo photo cells followed by a comparison of their output currents.

In the same article, other scanning techniques with oscillating slitsand with perforated discs are also described. In such techniques, thereflected or transmitted light only serves as source signals which aretransduced into electrical pulses, which after processing byconventional electrical techniques, are processed into the desiredinformation of the scanned surface. Typical circuits for processing thephoto-electric signal can comprise bridges and differentiating circuitsfor carrying out zero tuning of threshold value circuits for determiningmaximum or minimum values, or of time measuring circuits for measuringpulse widths or pulse spacings.

These prior processes are characterized with various disadvantages bywhich errors can result as for example, by aging of the photo-electriccells, which particularly in connection with zero tuning processes, cancreate considerable error in the results obtained. Additionally, suchsystems are characterized with delays in operation and tolerances in theresult which have been a deterent for their use in various applications.

SUMMARY OF THE INVENTION It is, accordingly, an object of this inventionto provide a measurement system where the processing of information inthe form of light values is performed optically in the initial stage soas to provide optical control signals which may then be transduced intoelectrical control signals.

In accordance with this invention, this is accomplished by a method andsystem for optical tuning with light spot scanner, particularly forindicating edge finding in connection with measuring microscopes,characterized in that the surface to be evaluated is scanned byalternate illumination of two configurations of light beams,semiadditive in nature, which on modulation by the surface result in achange of intensities which when transcribed provide information of thereflectivity or transparency of the surface.

Another object of this invention is characterized in 7 that the ratio ofthe varying optical properties of the surface and of the lightintensities, are correlated" to each other in such a manner that thedifference of the reflected and/or transmitted light beams disappearsupon periodic alternating illumination of the surface to provideinformation with respect thereto.

A further object of this invention is characterized in that the surfaceunder examination is iluminated by an alternating configuration of lightbeams symmetrically imaged on the surface with respect to each other. Afurther object of this invention is characterized by an optical edgedetection system for detecting an edge separating areas of varyingoptical properties on a surface.

A further object of this invention is characterized by a lightdeflection system in which a single light beam source is modified intotwo different light beam configurations wherein in the firstconfiguration two spaced light beams are developed whereas in the secondconfiguration, the two light beams are combined into a single beamintermediate the spacing of the initial pair of beams. A still furtherobject of this invention is characterized by an edge detection system inwhich an alternate configuration light beam is modulated by a scannedsurface to provide information as to change in intensities whereby themaximum change in intensities provides an indication ofa gradient in theoptical properties of the scanned surface.

It is also an object of this invention to provide an edge detectionsystem characterized -by symmetrical illumination of the surface with analternate configuration of light beams for detection of an edge ofvarying optical properties (e.g. opaque and transparent) to result inmodulation of the light beams to represent a change in intensitiesthereof in the form of a sine wave in which the maximum change inintensities indicates the location of the edge dividing the opticalproperties of the surface.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following more particulardescription of the preferred embodiments of the invention as illustratedin the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 1A are drawingsillustrating signal curves obtained in known optical tuning processes;FIG. 2 is a schematic drawing illustrating the optical intensity ofalternate illumination by two configurations of light beams.

FIG. 3 is a drawing showing a signal curve obtained in accordance withthe optical zero tuning system of this invention, and FIGS. 4 to 9 aredrawings illustrating various embodiments of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT It is known from photometry thatthe tuning of the brightness of the luminescent surface and of thecomparison surface at the same brightness can be performed with fargreater precision than the tuning of a luminescent surface forbrighteness maximum or minimum. It is also known, from he field,measuring fied, that a frequency can be measured more exactly byoverlapping with a comparison frequency and tuning to a beat frequencyzero, than by resonance tuning with a oscillating circuit. The reasonfor these differences in precision is shown in FIGS. 1 and 1A. In a zerotuning process, ccording to FIG. 1, a measuring signal y shows itshighest gradient at the position of the zero crossing, so that the zerotuning can be carried out with optimum sensitivity. However, as seenfrom the single curve y shown in FIG. 1A, tuning for maximum or minimum,is independent, or substantially independent, of the variable x. Thishas the effect of a relatively high measuring error, independent ofwhether the tuning is done manually or automatically.

In known measuring microscopes, the beam probe for determing theoccurrence of an edge, is oscillated by suitable means so that thesecond derivative (as a function of the position coordinate) disappearsat the location of the highest ingredient of the reflection ortransmission. Here, the second derivative is formed electronically,which, specified above is characterized by several disadvantages.

FIG. 2, the curve illustrates, in accordance with this invention, thebrightness densities upon the alternate illumination of a plane with twoconfigurations of light beams with the first configuration illustratedby light beam having twice the brightness density of the illuminationobtained by each oflight beams 6 and 7 in the second configuration. Thesame alternate illumination is shown in the top portion of FIG. 3. Belowthe illumination curves in FIG. 3 is also illustrated five differentedge positions of an edge 2 in five steps of progression A through E asthe edge intersects light beams 5, 6 and 7 on passage therethrough.Immediately below, in FIG. 3, a curve is shown illustrating the changein light intensity as the edge 2 progresses through positions A throughE. This is followed by another curve illustrating the shape of thesignal generated by optical tuning upon passage of an edge through thealternate illumination by light beam 5 and with light beams 6 and 7.

This alternating configuration of light probes insures a zero crossingof the alternating light probes at the moment when the bright-dark edge2, to be located, coincides with the symmetry line 3 of he light probes.In the lower-most portion of FIG. 3, the overall shape of the signal isdescribed as a function of the edge position.

For purposes of explanation in conjunction with FIG. 3, it may beassumed that an edge 2 of an opaque surface is moving in a positive xdirection to intersect light beams 5, 6 and 7 in their two alternatingconfigurations all sensed by a suitable detector, e.g. photo detector,to provide an indication in a change in intensity and/or rate of changeof intensity. In the original position of edge 2 at A light beams 5, 6and 7, in their alternating arrangements, are imaged on a transparentportion of the surface, or moving plane, to the detector. As will berecalled, the light beams 6 and 7 are imaged together in spacedrelationship in one configuration with equal intensity, and light beam5, in the alternate configuration, represents the combined or additivecombination 5 of light beam 6 and 7 so its intensity will be equal tothe 10 B, it continuously screens corresponding portions of light beam 6from the detector, while leaving unaffected the total intensity of lightbeam 5 or the light intensity of 7. This increasing change in intensity(as it screens light beam 6) is shown in FIG. 3, as is also the *'rateof change in intensity. As the edge continues to LII move to position C(with light beam 6 screened out) the difference in intensities betweenthe available illumination with light beams 6 and 7 and light beam 5continues to increase until, at position C, only half the illuminationof beam 5 is imaged in the one configuration and all of beam 7 allowedto image in the alternate configuration. Since half of the lightintensity of light beam 5 is equal to the light intensity of light beam7, the difference in illumination, sensed by detector, becomes zero andthus momentarily results in no change in intensity at position C. Thisminimum change in intensity is shown in FIG. 3 as well as the maximumrate of change of intensity at this minimum.

As the edge 2 continues to move to position D, it continues to screenout additional portions of light beam 5, resulting again in a change ofintensity where the intensity of light beam 7 surpasses the decreasingintensity of light beam 5. In a subsequent movement of light edge 2 toposition IE, it continues to screen successive portions of light beam 7so as to completely blank it out at its final point of travel. Atposition E, both light beam configurations (light beam 5 of oneconfiguration and light beams 6 and 7 in the other configuration) areall screened out resulting in no difference in light intensity duringalternating projections of the two light beam configurations.

As will be evident, the'maximum value of the gradient of the rate ofchange of intensity in the zero vicinity crossing, depends solely on thesharpness of the imaging of the middle light beam probe 5. This gradientwill normally remain'slightly below optimum value when, in the interestof minimum overall single width, a very small spacing between light beamprobes 6 and 7 is selected.

In this manner, strong overlapping of the individual components of theight probe configurations as well as a consequent overall decrease ofthe maximum amplitude of the signal is obtained. A minimum signal widthis desirable in those cases where line widths or line spacing are to bemeasured which are in the order of the edge signal width itself. Thearrangement as shown in FIGS. 2 and 3 represent a compromisetherebetween where the maximum of a double light beam probes 6 and 7coincide with the first secondary minimum of the individual light probe5. For example, if an objective of a numeric apperature N. A. 0.6 isused and the light of a HeNe laser with )t -*0.63 microns is employed,the overall single width is represented by the fonnula B 2 X I.22A/N.A.assuming an edge of ideal sharpness.

In FIGS. 4 to 9, various embodiments are shown for incorporating theforegoing as will be described below.

In the embodiment shown in FIG. 4, the system includes a lens 10,birefringement crystals 11 and 12, an electroptic rotating element 13, aHigh Frequency voltage source 14, (typically of the order of 5megahertz), a quarterwave plate 15, a lens 16, and a support 17,typically transparent, moveable in two directions X Y perpendicularly toeach other and vertically to the beam direction, a surface 18, (forexample, transparent) to be analyzed with a line 19 (e.g. opaque)carried on the surface. Lens with a focal plane 10f transmits a lightbeam 9 which is linearly polarized at 45 to the viewing plane, e.g. thedrawing plane, by suitable means, such a source of linearly polarizedlight and a quarter-wave plate. The birefringement crystal l1, typicallycalcite, is cut and aligned in such a manner that it will transmit aportion of light beam 9 undeflected as an ordinary beam 0, and a portionof light beam 9 in deflection at a predetermined angle as anextraordinary beam ao. An eIectro-optic arrangement 13 of a crystalshowing the longitudinal electro-optic effect (e.g. of potassiumdihydrogen phosphate crystal) is provided at its opposite surfaces withtransparent electrodes. These electrodes are energized by means ofa HighFrequency alternating voltage source 14 (e.g. 5 megahertz) so as torotate the ordinary and extraordinary beams, respectively 0 and a0,between one-fourth )t and three-fourths A increments. Any of theconventional rotators may be used as for example, those disclosed in U.S. Pat. Nos. 3,375,052 and 3,499,700. The electro-optic rotating element13 is arranged in such a manner, with respect to the poloraziationplanes of the ordinary and extraordinary beams leaving birefringementcrystal 11, that these beams, upon energization of optical rotator 13,are split into two components which are polarized vertically withrespect to each other with the mutual phase positions shifted againsteach other during the one halfwave of the High Frequency alternatingsource in one direction, and during the other half-wave in the otherdirection by one-fourth A.

The consequence thereof is that the ordinary beams 0 which leavesbirefringement crystal 11 in a linearly polarized manner vertically tothe drawing plane is changed, upon a positive halfwave of High Frequencyalternating voltage ll4l into a left-handed circularly polarizedradiation, and during the negative half-wave of High Frequencyalternating source 14 into a righthanded circularly polarized radiation.

The extraordinary beam ao leaving birefringement crystal 11 in apolarized manner parallel to the drawing plane is changed in theelectro-optic rotator element 13 during the positive halt wave of HighFrequency alternating voltage source 14!- into a right-handed circularlypolarized beam, and during the negative half-wave of High Frequencyalternating voltage source 14 into a left-handed circularly polarizedbeam.

The system also includes a quarter-wave plate 15 which is cut andaligned in such a manner that the radiation leaving birefringementcrystal 11 as an ordinary beam 0, after passing it through electro-opticelement 13, leaves the quarterwave plate 15 during a positive half-waveof High Frequency alternating voltage source 14, as a radiation which isvertically polarized to the drawing plane, and during a negativehalf-wave of High Frequency alternating voltage M, as radiation which ispolarized parallel to the drawing plane.

The light beam leaving birefringement crystal 11 as an extraordinarybeam ao, leaves the quarter-wave plate 15, after having passed throughthe electro-optic rotator element 13, during a positive half-wave ofHigh Frequency alternating voltage source 14, as irradiation which ispolarized parallel to the drawing plane, and during a negative half-waveof High Frequency alternating voltage source 14 as irradiation which ispolarized vertically to the drawing plane. As a result, the irradiationin birefringement crystal 11 as an ordinary beam 0 is transmittedthrough birefringement crystal 12, during a positive half-wave of HighFrequency alternating voltage source 14, undeflected as an ordinarybeam, whereas the radiation leaving birefringement crystal 11 as anextraordinary beam ao is deflected in birefringement crystal 12 in sucha manner that it joins or merges with the radiation leaving thebirefringement crystal as an ordinary beam 0 at a single exit site onthe exit face of crystal 12. During the negative half-wave of thevoltage supplied by the High Frequency alternating voltage source 14,the radiation leaving birefringement crystal 11 as an ordinary beam 0,is deflected in birefringement crystal 12 as an extraordinary beam a0,whereas the radiation leaving crystal 11 as an extraordinary beam a0,penetrates the birefringement crystal l2, owing to the position of itspolarization plane, undeflected as an ordinary beam at a different exitsite on the exit face of crystal 12.

In operation, during a negative half-wave cycle of the voltage eneratedby High Frequency source 14, lens 16 images on surface 18 two points ofillumination which are symmetrical to an illumination point imagedduring a positive half-wave cycle of source 14. Upon shifting of support17 to the right, line 19 reaches the range of the light probes formed bycombinations of light beams 5, 6 and 7 formed during the alternateconfiguration of the light beams exiting from crystal 12 at threedifferent space points. The indication of edge finding takes place inthe manner described in connection with the description of FIG. 3.

The embodiment showing in FIG. 5 is substantially of the same structure,with the exception of the fact that birefringement crystals 11 and 12are replaced by Wol Iaston prisms 11w and 12w. The radiation representedby beam 9 and linearly polarized to the drawing plan at an angle of 45is split in Wollaston prism 11w into one component which is polarizedvertically to the drawing plane into a second component polarized in aplane parallel to the drawing plane. In theelectro-optic rotatingelement 13, which is of the same design as em ployed in system of FIG.4, the two light beam components are split into extraordinary andordinary beams. By the energization of the electro-optic rotatingelement 13, by means of a High Frequency alternating voltage source 14generating a so-called quarter-wave voltage, the ordinary beams areshifted with respect to the extraordinary beams in a manner well-knownin the art, if there is a positive half-wave of High Frequencyalternating voltage source 14 by quarter-wave in one direction andconversely if there is a negative half-wave voltage at the same voltagesource, by quarter-wave in the other direction with respect to eachother. This has the consequence that the beam leaving the Wollastonprism 11w vertically polarized to the drawing plane leaves theelectro-optic rotating element 13 in a lefthanded circular polarizedmanner if there is a positive half-wave of High Frequency fromalternating voltage source 14, whereas, the other beam leaves theelectrooptic element 13 in a right-handed circular polarized manner. Ifthere is a negative half-wave of High Frequency from alternating voltagesource E4, the first beam leaves the electro-optic rotating element 113in a right-handed circular polarization, whereas the other beam leavesthis element in a left-hand circular polarization. Upon leaving thequarterwave plate 15, the two beams, on a positive half-wave of HighFrequency from alternating source M are polarized verticaly and inparallel to the drawing plane. Conversely, if there is a negativehalf-wave, they are polarized in parallel and vertical planes to thedrawing plane. After passing through lens 20, the light beams reach asecond Wollaston prism 12w and leave, according to the state ofpolarization, either as an individual beam coinciding with the opticalaxis, or as two laterally extending beams, so as to generate either asingle beam probe 5 or as double beam probe 6 and 7 on surface 18.

FIG. 6 shows a still further embodiment of the invention. In the systemshown here, monochromatic radiation emanating from the light source 21is transmitted by a collimator lens 22 and an aperture plate 23 to entera first light deflector 24, which similarly to a second light deflector27, is comprised of a plurality of deflector stages each containing anelectro-optically controllable rotator and a birefringement crystal. Ananalogous arrangement of deflectors and rotators may be found in theaforeindicated U. S. Pat. No. 3,499,700.

Following the ight deflector 24, a mask 26 is provided which asindicated in FIG. 6A, is comprised of an opaque layer with a series oftransparent zones. Following mask 26, is a second light deflector 27, abeam splitter 28, a lens 29 and a support 17, which can be shifted intwo directions vertically to each other, as well as vertically to thebeam direction, and which carries a surface 18 and a line 19 to beanalyzed. The two light deflectors 24 and 27 are operated by aconventional electronic control arrangement 25 in such a manner that thebeam leaving the first light deflector penetrates one respective zone ofmask 26, and then the beam carrying the information is further deflectedby the second light deflector 27 in a complementary manner so that itenters beam splitter 28 at a same spot each time.

By suitable programming the electronic control 25, the beams leaving thefirst beam deflector 24 can, for example, be directed alternately tofields 260 and 26d of mask 26, so that on surface 18 one respectivesingle gap and a double gap of the same overall surface is oscillatedsymmetrically in an alternate manner. The light reflected at surface 18or line 19, respectively, is retransmitted through lens 29 a second timeand is a partly projected by beam splitter 28 in the direction of thelight detector 30. If the edge of line 19 gets into the symmetry line ofthe light beam probe configurations, periodically imaged on surface 18,the voltage at output 31 of photodetector 30 will equal zero forindicating the disappearance of the second derivitive.

If the electronic control 25 is programmed in such a manner that thefields 26a and 26b of mask 26 are alternately selected by the beamprobe, the image of a horizontal and of a vertical rectangle isalternately oscillated in imaging on surface 18 as shown in FIG. 8. If ascanned edge reaches the symmetry line of the light beam configurations,the signal appearing at output 311 of light detector 30 disappears also.It is equally possible to perform the scanning by means ofa spotarrangement as shown in FIG. 9. With such an arrangement, it is possibleto determine the symmetry position with respect to edges extending intwo directions which are perpendicular to each other. For generating thespot arrangement, the electronic control 25 of the embodiment shown inFIG. 6 may be programmed in such a manner that fields 26e, 26f arealternately selected by the beam probe. It is to be understood thatother spot and gap patterns are equally possible, as, for example, theindividual gaps can show different lengths, different intensities anddifferent symmetry positions with respect to each other. This appliesequally to the spot arrangement as referred to in FIG. 9. The lightreflected at surface 18 can be evaluated by means of any conventionalcircuitry. It is, of course, equally possible to perform the evaluationwith different transparencies of surface 18. In FIGS. 4 and 5, the beamsplitters and light detectors necessary for automatic evaluation havebeen omitted so as to render the representation less complicated.

FIG. 7 shows a further embodiment of the invention which includes alight source 41, a condenser 42, a semiconductor mask 43 to be measured,a microscopic objective &4, and a photodetector arrangement 45. Thephoto-detector arrangement 45 is illustrated in FIG. 7A wherein it isshown to include four detectors 45a, 45b, 45c and 45d. The terminalsmarked U11 and U2 are connected to the inputs of a differentialamplifier 46 (FIG. 78) from which the output signal will equal zero whenthe edge of the line drawn on mask 43 reaches a symmetry line 47 of thedetector arrangement 45 Unlike previous embodiments, this embodimentdiffers to the dynamic processes of the first three embodiments by beinga static application.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formerdetails may be made therein without departing from the spirit and scopeof the invention.

What is claimed is:

l. A light beam deflection system comprising:

A. means for producing a beam of plane polarized light;

B. means for rotating the plane of polarization of said beam to twointermediate coexisting mutually orthogonal planes of polarization;

C. first birefringent means for passing said rotated beam therethroughin a first configuration of two polarized beams having a respective oneof two spaced perpendicular polarized planes, along a corresponding oneof two different paths;

D. electro-optic control means alternately settable between a. a firststate maintaining said first configuration of perpendicular planes ofpolarized beams, and

b. a second state for circular polarization thereof in their respectivebeam paths;

E. means for linearly polarizing the circularly polarized beams in tworespective mutually orthogonal in phase beam planes; and

F. second birefringent means having parallel entrance and exit faces forpassage therethrough of said beam paths with said beam paths a. in saidfirst configuration having a first of said beam paths with one plane ofpolarization of said beam paths passing in an undeflected path and theother of said beam path having a perpendicular plane of polarizationdeflected into convergence with said first beam path at a first exitsite on the exit face of said second birefringent means, and

b. in said second rotated configuration having the said second beam pathwith the rotated plane of polarization passing in an undeflected path toa second exit site on said exit face spaced from said first exit site onone side thereof, and the said first beam path with its rotated andperpendicular plane of polarization deflected in divergence from saidfirst beam path at a third exit site on said exit face spaced from saidsecond exit site and from said first exit site on the opposite sidethereof.

2. The system of claim 1 wherein said spaced second and third exit sitesare symmetrically spaced on opposite sides of said first exit site.

3. The system of claim ll wherein said control means comprises means foroscillation between said first and second states.

4. The system of claim 11 wherein said control means comprises means forHigh Frequency oscillation between said first and second states.

5. The system of claim 1 wherein the first said rotat ing means rotatesthe beam 45 intermediate said two mutually orthogonal planes ofpolarization.

6. The system of claim ll including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

7. The system of claim 6 wherein said sensing means comprises detectionof the maximum change in intensities of said first, second and thirdexit beams as said edge passes therethrough.

8. The system of claim 2 wherein said control means comprises means foroscillation between said first and second states.

9. The system of claim 8 wherein the first said rotating means rotatesthe beam 45 intermediate said two mutualy orthogonal planes ofpolarization.

E0. The system of claim 9 including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

Ill. The system of claim 10 wherein said sensing means comprisesdetecting of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.

12. The system of claim 8 including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

13. The system of claim 12 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.

14. The system of claim 2 wherein the first said rotating means rotatesthe beam 45 intermediate said two mutually orthogonal planes ofpolarization.

115. The system of claim 14 including 5 A. sensing means in registerwith said first, second and third exit beams for detecting theintensities thereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

16. The system of claim 15 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.

17. The system of claim 2 including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

18. The system of claim 17 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.

19. The system of claim 2 wherein said control means comprises means forHigh Frequency oscillation between said first and second states.

20. The system of claim 19 wherein the first said rotating means rotatesthe beam 45 intermediate said two mutually orthogonal planes ofpolarization.

21. The system of claim 20 including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

22. The system of claim 21 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.

23. The system of claim 19 including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

24. The system of claim 23 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.

25. The system of claim 3 wherein the first said rotating means rotatesthe beam 45 degrees intermediate said two mutually orthogonal planes ofpolarization.

26. The system of claim 25 including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

27. The system of claim 26 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.

Ill

28. The system of claim 3 including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

29. The system of claim 28 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.

30. The system of claim 4 wherein the first said rotating means rotatesthe beam 45 intermediate said two mutually orthogonal planes ofpolarization.

N 31. The system of claim 3Q including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and

B. means for passing an edge of different optical properties on a planeparallel to said exit face and intersecting said first, second and thirdexit beams.

32. The system of claim 31 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.

33. The system of claim 4 including A. sensing means in register withsaid first, second and third exit beams for detecting the intensitiesthereof, and B. means for passing an edge of different opticalproperties on a plane parallel to said exit face and intersecting saidfirst, second and third exit beams. 34. The system of claim 33 whereinsaid sensing means comprises detection of the maximum change inintensities of said first, second and third exit beams as said edgepasses therethrough.

35. The system of claim 5 including A. sensing means in register withsaid first, second said edge passes therethrough.

and third exit beams for detecting the intensities

1. A light beam deflection system comprising: A. means for producing abeam of plane polarized light; B. means for rotating the plane ofpolarization of said beam to two intermediate coexisting mutuallyorthogonal planes of polarization; C. first birefringent means forpassing said rotated beam therethrough in a first configuration of twopolarized beams having a respective one of two spaced perpendicularpolarized planes, along a corresponding one of two different paths; D.electro-optic control means alternately settable between a. a firststate maintaining said first configuration of perpendicular planes ofpolarized beams, and b. a second state for circular polarization thereofin their respective beam paths; E. means for linearly polarizing thecircularly polarized beams in two respective mutually orthogonal inphase beam planes; and F. second birefringent means having parallelentrance and exit faces for passage therethrough of said beam paths withsaid beam paths a. in said first configuration having a first of saidbeam paths with one plane of polarization of said beam paths passing inan undeflected path and the other of said beam path having aperpendicular plane of polarization deflected into convergence with saidfirst beam path at a first exit site on the exit face of said secondbirefringent means, and b. in said second rotated configuration havingthe said second beam path with the rotated plane of polarization passingin an undeflected path to a second exit site on said exit face spacedfrom said first exit site on one side thereof, and the said first beampath with its rotated and perpendicular plane of polarization deflectedin divergence from said first beam path at a third exit site on saidexit face spaced from said second exit site and from said first exitsite on the opposite side thereof.
 2. The system of claim 1 wherein saidspaced second and third exit sites are symmetrically spaced on oppositesides of said first exit site.
 3. The system of claim 1 wherein saidcontrol means comprises means for oscillation between said first andsecond states.
 4. The system of claim 1 wherein said control meanscomprises means for High Frequency oscillation between said first andsecond states.
 5. The system of claim 1 wherein the first said rotatingmeans rotates the beam 45* intermediate said two mutually orthogonalplanes of polarization.
 6. The system of claim 1 including A. sensingmeans in register with said first, second and third exit beams fordetecting the intensities thereof, and B. means for passing an edge ofdifferent optical properties on a plane parallel to said exit face andintersecting said first, second and third exit beams.
 7. The system ofclaim 6 wherein said sensing means comprises detection of the maximumchange in intensities of said first, second and third exit beams as saidedge passes therethrough.
 8. The system of claim 2 wherein said controlmeans comprises means for oscillation between said first and secondstates.
 9. The system of claim 8 wherein the first said rotating meansrotates the beam 45* intermediate said two mutualy orthogonal planes ofpolarization.
 10. The system of claim 9 including A. sensing means inregister with said first, second and third exit beams for detecting theintensities thereof, and B. means for passing an edge of differentoptical properties on a plane parallel to said exit face andintersecting said first, second and third exit beams.
 11. The system ofclaim 10 wherein said sensing Means comprises detecting of the maximumchange in intensities of said first, second and third exit beams as saidedge passes therethrough.
 12. The system of claim 8 including A. sensingmeans in register with said first, second and third exit beams fordetecting the intensities thereof, and B. means for passing an edge ofdifferent optical properties on a plane parallel to said exit face andintersecting said first, second and third exit beams.
 13. The system ofclaim 12 wherein said sensing means comprises detection of the maximumchange in intensities of said first, second and third exit beams as saidedge passes therethrough.
 14. The system of claim 2 wherein the firstsaid rotating means rotates the beam 45* intermediate said two mutuallyorthogonal planes of polarization.
 15. The system of claim 14 includingA. sensing means in register with said first, second and third exitbeams for detecting the intensities thereof, and B. means for passing anedge of different optical properties on a plane parallel to said exitface and intersecting said first, second and third exit beams.
 16. Thesystem of claim 15 wherein said sensing means comprises detection of themaximum change in intensities of said first, second and third exit beamsas said edge passes therethrough.
 17. The system of claim 2 including A.sensing means in register with said first, second and third exit beamsfor detecting the intensities thereof, and B. means for passing an edgeof different optical properties on a plane parallel to said exit faceand intersecting said first, second and third exit beams.
 18. The systemof claim 17 wherein said sensing means comprises detection of themaximum change in intensities of said first, second and third exit beamsas said edge passes therethrough.
 19. The system of claim 2 wherein saidcontrol means comprises means for High Frequency oscillation betweensaid first and second states.
 20. The system of claim 19 wherein thefirst said rotating means rotates the beam 45* intermediate said twomutually orthogonal planes of polarization.
 21. The system of claim 20including A. sensing means in register with said first, second and thirdexit beams for detecting the intensities thereof, and B. means forpassing an edge of different optical properties on a plane parallel tosaid exit face and intersecting said first, second and third exit beams.22. The system of claim 21 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.
 23. The system ofclaim 19 including A. sensing means in register with said first, secondand third exit beams for detecting the intensities thereof, and B. meansfor passing an edge of different optical properties on a plane parallelto said exit face and intersecting said first, second and third exitbeams.
 24. The system of claim 23 wherein said sensing means comprisesdetection of the maximum change in intensities of said first, second andthird exit beams as said edge passes therethrough.
 25. The system ofclaim 3 wherein the first said rotating means rotates the beam 45degrees intermediate said two mutually orthogonal planes ofpolarization.
 26. The system of claim 25 including A. sensing means inregister with said first, second and third exit beams for detecting theintensities thereof, and B. means for passing an edge of differentoptical properties on a plane parallel to said exit face andintersecting said first, second and third exit beams.
 27. The system ofclaim 26 wherein said sensing means comprises detection of the maximumchange in intensities of said first, second and third exit beams as saidedge passes therethrough.
 28. The system of claim 3 including A. sensingmeans in register with said first, second and third exit beams fordetecting the intensities theReof, and B. means for passing an edge ofdifferent optical properties on a plane parallel to said exit face andintersecting said first, second and third exit beams.
 29. The system ofclaim 28 wherein said sensing means comprises detection of the maximumchange in intensities of said first, second and third exit beams as saidedge passes therethrough.
 30. The system of claim 4 wherein the firstsaid rotating means rotates the beam 45* intermediate said two mutuallyorthogonal planes of polarization.
 31. The system of claim 30 includingA. sensing means in register with said first, second and third exitbeams for detecting the intensities thereof, and B. means for passing anedge of different optical properties on a plane parallel to said exitface and intersecting said first, second and third exit beams.
 32. Thesystem of claim 31 wherein said sensing means comprises detection of themaximum change in intensities of said first, second and third exit beamsas said edge passes therethrough.
 33. The system of claim 4 including A.sensing means in register with said first, second and third exit beamsfor detecting the intensities thereof, and B. means for passing an edgeof different optical properties on a plane parallel to said exit faceand intersecting said first, second and third exit beams.
 34. The systemof claim 33 wherein said sensing means comprises detection of themaximum change in intensities of said first, second and third exit beamsas said edge passes therethrough.
 35. The system of claim 5 including A.sensing means in register with said first, second and third exit beamsfor detecting the intensities thereof, and B. means for passing an edgeof different optical properties on a plane parallel to said exit faceand intersecting said first, second and third exit beams.
 36. The systemof claim 35 wherein said sensing means comprises detection of themaximum change in intensities of said first, second and third exit beamsas said edge passes therethrough.